The invention concerns a device for sorting small articles by size, with a chute for conveying the articles and with a gap that allows articles of less than a prescribed size through it between the chute and a mechanism that extends across the slide and detaches and conveys larger articles away along the gap.
Devices of this type are employed in particular to sort plastic articles leaving extruders. These articles include both finished pieces and waste. The invention accordingly especially concerns a device for separating the articles leaving an extruder into product and sprue.
In one known device of this genus, a belt or other appropriate conveyor delivers the articles being sorted to the top of a chute. They slide down between it and a conveyor screw positioned across the slope of the chute and at a distance from it. A motor rotates the screw in a direction opposite the slope. The worm is far enough from the chute to allow smaller articles through. The screw carries the larger articles off to one side.
Prerequisite to this method of sorting of course is that the parts that are to be separated differ at least to some extent in size. This prerequisite is practically always satisfied by extruded-plastic articles in that the products are almost always compact articles while the sprues are comparatively bulky.
One situation does affect the capacity to separate products from waste, however. Sometimes the former hook together and fail to drop through the gap between the chute and the screw, which carries them off to the side. This occurrence undesirably increases the rejection rate. One remedy comprises providing the screws with prongs that extend over the threads. The prongs intercept the hooked-together articles and lift them off the chute to release them.
The rate of separation attainable with screws of this type has not been satisfactory, and sorting devices with oscillating chutes have been tried. The system was intended to allow transverse conveyance along the length of a cylinder separated from the chute and to ensure separation due to the oscillation. This device did provide better separation and hence sorting than the aforesaid device. It was, however, still not absolutely satisfactory when the articles were complicated in shape. It has accordingly not yet been possible to satisfy all practical requirements as to the separation of product from waste.